The ascendancy of eosinophil counts in non-small cell lung cancer: a potential marker for predicting response and survival under nivolumab treatment.

Lung cancer is the leading cause of cancer-related death globally and is often diagnosed at an advanced stage. Nivolumab represents a significant advancement for treating advanced non-small cell lung cancer (NSCLC). However, the absence of reliable biomarkers predicting treatment response hinders personalized therapy. Eosinophils play a notable role in cancer biology, particularly when treated with immune checkpoint inhibitors. Eosinophils can infiltrate tumor tissues, directly interacting with tumor cells or modifying the tumor microenvironment. This study aims to assess the potential of PD-L1 expression and peripheral blood eosinophil count in predicting treatment response and patient survival. This retrospective cohort study was conducted in three major cancer centers in Turkey, including 174 advanced NSCLC patients who had progressed after chemotherapy between July 2019 and November 2023. Demographic and clinical data, PD-L1 levels, and eosinophil counts were analyzed using SPSS 27.0. Survival analyses were performed with Kaplan-Meier and Cox regression models. Increased peripheral blood eosinophil count was positively associated with response to Nivolumab treatment and overall survival. Among treatment responders, 54.1% had eosinophil levels between 100-499 cells/mm³ before treatment, increasing to 70.8% post-treatment. In patients with high PD-L1 positivity (>50%), eosinophil levels averaged 266.0 cells/mm³, with improved survival outcomes (mean survival: 24.06 months, median: 20.0 months). Non-responders had a mean survival of 19.05 months and a median survival of 15.2 months. Peripheral eosinophil count appears to be a potential biomarker for predicting response to Nivolumab treatment and survival in NSCLC patients. Combined evaluation of eosinophil count and PD-L1 expression may enhance personalized treatment strategies. Further validation in prospective, randomized studies is necessary.